The present invention relates to a linear measuring device having a scale that is uncoupled from its mounting fixture, in particular, the scale can move relative to the mounting fixture so that deformations of the mounting fixture are not transmitted to the scale.
A linear measuring device is described in the European Patent 0 264 801 B1. To avoid scale deformations caused by forces resulting from the different thermal linear expansion of the scale and of its mounting fixture, and from the manner in which the scale is mounted, the scale is supported at its Bessel points. This mounting arrangement is implemented by a ball bearing arrangement where the balls are retained so as to permit rolling motion, and by a lateral longitudinal guidance using other balls. One of these other balls fixes the scale in place with respect to the mounting fixture in the measuring direction. Springs are provided to maintain the contact pressure between the scale and the balls, as well as between the mounting fixture and the balls.
In the European Patent described, the arrangement does not ensure that the scale is held in its mounting fixture in a manner that is free of constraining forces. The transfer of deformations in the mounting fixture to the scale thus cannot be ruled out.
The present invention is a linear measuring device with a scale supported in its mounting fixture in a manner that is free of extraneous forces to the greatest possible extent, and which minimizes the influence of deformations in the mounting fixture, and thus improves the measuring accuracy.
In one embodiment, the invention is a linear measuring device that includes a scale, a scale graduation disposed on the scale, and a mount fixture holding the scale, said mount fixture being rigidly coupled to the scale in the measuring direction at a first point, and being movably coupled at additional points in the measuring direction. At least the first point is disposed in a neutral plane of the mount fixture containing a neutral axis of the mount fixture, and the scale graduation is disposed in a second plane of the scale parallel to the neutral plane of the mount fixture.
In the linear measuring device, the scale is uncoupled from its mounting fixture, and is optimally fixed to the mounting fixture, as required. In response to temperature changes, the scale is able to move with respect to its mounting fixture in a manner that is substantially free of forces, so that mounting fixture deformations are not transferred to the scale.